Fuel oil compositions

ABSTRACT

Additive compositions comprising an ethylene/vinyl acetate or propionate/vinyl branched carboxylate terpolymer and an ethylene-unsaturated ester copolymer improve the low temperature properties of fuel oils.

This Application is a 371 of PCT/EP95/04805 filed Dec. 5, 1995.

This invention relates to oil compositions, primarily to fuel oilcompositions, and more especially to fuel oil compositions susceptibleto wax formation at low temperatures, and to additive compositions forsuch fuel oil compositions.

Fuel oils, whether derived from petroleum or from vegetable sources,contain components that at low temperature tend to precipitate as largecrystals or spherulites of wax in such a way as to form a gel structurewhich causes the fuel to lose its ability to flow. The lowesttemperature at which the fuel will still flow is known as the pourpoint.

As the temperature of the fuel falls and approaches the pour point,difficulties arise in transporting the fuel through lines and pumps.Further, the wax crystals tend to plug fuel lines, screens, and filtersat temperatures above the pour point. These problems are well recognizedin the art, and various additives have been proposed, many of which arein commercial use, for depressing the pour point of fuel oils.Similarly, other additives have been proposed and are in commercial usefor reducing the size and changing the shape of the wax crystals that doform. Smaller size crystals are desirable since they are less likely toclog a filter. The wax from a diesel fuel, which is primarily an alkanewax, crystallizes as platelets; certain additives inhibit this, causingthe wax to adopt an acicular habit, the resulting needles being morelikely to pas through a filter than are platelets. The additives mayalso have the effect of retaining in suspension in the fuel the crystalsthat have formed, the resulting reduced settling also assisting inprevention of blockages.

A further problem encountered at temperatures low enough for wax to formin a fuel is the settlement of the wax to the lower region of anystorage vessel. This has two effects; one in the vessel itself where thesettled layer of wax may block an outlet at the lower end, and thesecond in subsequent use of the fuel. The composition of the wax-richportion of fuel will differ from that of the remainder, and will havepoorer low temperature properties than that of the homogeneous fuel fromwhich it is derived.

There are various additives available which change the nature of the waxformed, so that it remains suspended in the fuel, achieving a dispersionof waxy material throughout the depth of the fuel in the vessel, with agreater or lesser degree of uniformity depending on the effectiveness ofthe additive on the fuel.

Although the way in which CFPP depressants and wax anti-settlingadditives function is not completely understood, there is evidence thattheir effectiveness depends to a significant extent on matching of thealkanes in the fuel to alkyl or alkylene chains in the additive, thegrowth of the alkane wax crystals being affected, for example, by theco-crystallization of an alkyl chain of similar length in an additive.

EP-A-493,769 describes the use of certain terpolymers as additives forpetroleum distillates, in particular their use in improving theflowability of middle distillates as measured by the Cold FilterPlugging Point (CFPP) test. The terpolymers are made by polymerisingethylene, vinyl acetate, and vinyl neo-nonanoate or decanoate.

A problem in using said terpolymers is that, although their CFPPperformance is satisfactory immediately after they are used to treat adistillate fuel, the CFPP performance of a so-treated fuel deteriorateswith time. Such deterioration over time is referred to herein as `CFPPregression`.

The present invention provides a way of meeting the problem of CFPPregression encountered with such terpolymers, by use of a specificco-additive. Through use of such a co-additive, excellent CFPPperformance is also achieved.

Thus, a first aspect of the invention is an oil-soluble additivecomprising components (A) and (B) wherein

(A) is an ethylene terpolymer having, in addition to units derived fromethylene, units of the formula: ##STR1## and units of the formula##STR2## wherein R¹ and R², which may be the same or different, eachrepresents H or methyl;

R³ represents an alkyl group having up to 4 carbon atoms; and

R⁴ represents a tertiary alkyl group having 8 or more carbon atoms; and

(B) is an ethylene-unsaturated ester copolymer, different from (A),having a number average molecular weight in the range of 1,200 to 20,000and an ester content of 0.3 to 17 molar per cent, provided that saidester content is at least 2 molar per cent lower than that of the estersin (A), or any other nucleating cold flow additive.

A second aspect of the invention is a composition comprising a fuel oiland an additive as defined in the first aspect of the invention.

A third aspect of the invention is an additive concentrate compositioncomprising an additive as defined in the first aspect of the inventionand a liquid carrier in admixture therewith.

A fourth aspect of the invention is the use of an additive of the firstaspect of the invention or a concentrate composition of the third aspectof the invention to improve the low temperature properties of an oil.

The examples herein will demonstrate the effectiveness of (B) inovercoming or at least reducing the above-mentioned problem of CFPPregression arising from the use of certain terpolymers.

The features of the invention will now be discussed in further detail asfollows.

COMPONENT (A)

The term "terpolymer", as used herein, requires the polymer to have atleast three different repeat units, i.e., be derivable from at leastthree different monomers, and includes polymers derivable from four ormore monomers. For example, the polymer may contain two or moredifferent units of the formula I or II, and/or may contain units of theformula ##STR3## wherein R⁵ represents a hydrocarbyl group having 5 ormore carbon atoms other than one as defined by R⁴.

As used in this specification the term "hydrocarbyl" refers to a grouphaving a carbon atom directly attached to the rest of the molecule andhaving a hydrocarbon or predominantly hydrocarbon character. Amongthese, there may be mentioned hydrocarbon groups, including aliphatic,(e.g., alkyl), alicyclic (e.g., cycloalkyl), aromatic, aliphatic andalicyclic-substituted aromatic, and aromatic-substituted aliphatic andalicyclic groups. Aliphatic groups are advantageously saturated. Thesegroups may contain non-hydrocarbon substituents provided their presencedoes not alter the predominantly hydrocarbon character of the group.Examples include keto, halo, hydroxy, nitro, cyano, alkoxy and acyl. Ifthe hydrocarbyl group is substituted, a single (mono) substituent ispreferred. Examples of substituted hydrocarbyl groups include2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl, 2-ketopropyl,ethoxyethyl, and propoxypropyl. The groups may also or alternativelycontain atoms other than carbon in a chain or ring otherwise composed ofcarbon atoms. Suitable hetero atoms include, for example, nitrogen,sulfur, and preferably oxygen. Advantageously, the hydrocarbyl groupcontains at most 30, preferably at most 15, more preferably at most 10and most preferably at most 8, carbon atoms.

The terpolymer may also contain units of formulae other than thosementioned above, for example units of the formula ##STR4## where R⁶represents --OH, or of the formula ##STR5## where R⁷ and R⁸ eachindependently represent hydrogen or an alkyl group with up to 4 carbonatoms, the units V advantageously being derived from isobutylene,2-methylbut-2-ene, 2-methylpent-2-ene, or di-isobutylene.

In units of the formula I which are preferably --CH₂ --CR¹ --OOCR³, R¹advantageously represents hydrogen, and R³ advantageously representsethyl or, especially, methyl. Advantageously R³ is not t-butyl, butotherwise may be straight-chain or branched. In units of the formula IIwhich are preferably --CH₂ --CR² OOCR⁴, R² advantageously representshydrogen. R⁴ may represent a tertiary alkyl group having from 8 to 15carbon atoms; preferably OOCR⁴ represents neononanoate or neodecanoate.

As indicated above, it is within the scope of the invention to provide aterpolymer containing a mixture of different species of R³ and/or R⁴. Itis also within the scope of the invention to provide a compositioncomprising a mixture of two or more terpolymers according to the firstaspect of the invention.

The ester-containing units of the terpolymer, more especially the unitsof Formulae I and II, advantageously represent from 2.3 to 35 molar percent of the polymer. The terpolymer is preferably the type known asarrestors, such as described in U.S. Pat. No. 3,961,916, in which theester groups advantageously constitute from 7.5 to 35 molar per cent,preferably from 10 to 25, and more preferably from 10 to 20, and mostpreferably 10 to 17, molar per cent. Preferably, the molar per cent is15 or more.

The molar proportion of the units of the formula I in the terpolymer ispreferably in the range of from 1 to 9 percent, and the molar proportionof the units of the formula II in the terpolymer is preferably in therange of from 4 to 13 percent.

The terpolymer advantageously has a number average molecular weight, Mn,as measured by gel permeation chromatography, of at most 20,000. Itsmolecular weight is, generally, at most 14,000, advantageously at most10,000, more advantageously in the range of 1,400 to 7,000, preferably3,000 to 6,000 and most preferably from 3,500 to 5,500.

Preferably, the degree of branching (or linearity) of the terpolymer, asmeasured by proton NMR spectroscopy is less than 15, more preferably 10,most preferably 6 CH₃ groups per 100 CH₂ units. The linearity iscorrected for the number of terminal methyl groups, based on the numberaverage molecular weight (a relatively small correction) and, moreimportantly, for the number of methyl and methylene groups in the alkylgroups of the carboxylate side chains.

COMPONENT (B)

Without wishing to be bound by any theory, applicant believe thatcomponent (B) may function as a nucleating agent (or nucleator) such asdescribed in U.S. Pat. No. 3,961,916. Preferably, it is anethylene-unsaturated ester copolymer, for example where the unsaturatedester is a vinyl ester of a C₂ to C₁₀ aliphatic monocarboxylic acid suchas vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl n-hexanoate,vinyl n-octanoate, vinyl 2-ethyl hexanoate, vinyl C₉ or C₁₀ neo acidesters.

Preferably, the number average molecular weight of component (B) is upto 15,000, more preferably from 1,200 to 10,000 and most preferably from3,000 to 10,000.

The ester groups of component (B) advantageously represent up to 10,more advantageously from 0.3 to 7.5, and preferably from 3.5 to 7.0molar per cent thereof.

Preferably, the ester content of component (B) is at least 3 molar percent lower than the content of the esters in component (A).

(B) may contain other monomer units, to be a ter- or higher polymer.Examples of such other units include isobutylene and di-isobutylene.

Advantageously, the proportion by weight of component (B), based on theweight of (A) and (B) combined, is 10% or less, preferably in the rangeof 5% to 2%.

Examples of other nucleators are those known in the art such as thosewith polyoxyalkylene chains as described for example in EP-A-61,895;JP-2-51477 & 3-34790; EP-A-117,108; EP-A-326,356; and EP-A-356,256.

Examples of polyoxyalkylene compounds include polyoxyalkylene esters,ethers, ester/ethers and mixtures thereof, particularly those containingat least one, preferably at least two, C₁₀ to C₃₀ linear alkyl groupsand a polyoxyalkylene glycol group of molecular weight up to 5,000,preferably 200 to 5,000, the alkylene group in said polyoxyalkyleneglycol containing from 1 to 4 carbon atoms, as described in EP-A-61 895and in U.S. Pat. No. 4,491,455.

The preferred esters, ethers or ester/ethers which may be used maycomprise compounds in which one or more groups (such as 2, 3 or 4groups) of formula --OR²⁵ are bonded to a residue E, where E may forexample represent A (alkylene)q, where A represents C or N or is absent,q represents an integer from 1 to 4, and the alkylene group has from oneto four carbon atoms, A (alkylene)q for example being N(CH₂ CH₂)₃ ;C(CH₂)₄ ; or (CH₂)₂ ; and R²⁵ may independently be

(a) n-alkyl-

(b) n-alkyl-CO--

(c) n-alkyl-OCO--(CH₂)_(n) --

(d) n-alkyl-OCO--(CH₂)_(n) CO--

n being, for example, 1 to 34, the alkyl group being linear andcontaining from 10 to 30 carbon atoms. For example, they may berepresented by the formula R²³ OBOR²⁴, R²³ and R²⁴ each being defined asfor R²⁵ above, and B representing the polyalkylene segment of the glycolin which the alkylene group has from 1 to 4 carbon atoms, for example,polyoxymethylene, polyoxyethylene or polyoxytrimethylene moiety which issubstantially linear, some degree of branching with lower alkyl sidechains (such as in polyoxypropylene glycol) may be tolerated but it ispreferred that the glycol should be substantially linear.

Suitable glycols generally are substantially linear polyethylene glycols(PEG) and polypropylene glycols (PPG) having a molecular weight of about100 to 5,000, preferably about 200 to 2,000. Esters are preferred andfatty acids containing from 10 to 30 carbon atoms are useful forreacting with the glycols to form the ester additives, it beingpreferred to use C₁₈ to C₂₄ fatty acid, especially behenic acid. Theesters may also be prepared by esterifying polyethoxylated fatty acidsor polyethoxylated alcohols.

Polyoxyalkylene diesters, diethers, ether/esters and mixtures thereofare suitable as additives, diesters being preferred when the petroleumbased component is a narrow boiling distillate, when minor amounts ofmonoethers and monoesters (which are often formed in the manufacturingprocess) may also be present. It is important for active performancethat a major amount of the dialkyl compound is present. In particular,stearic or behenic diesters of polyethylene glycol, polypropylene glycolor polyethylene/polypropylene glycol mixtures are preferred.

FUEL OIL

The oil may be fuel oil such as a petroleum-based fuel oil, suitably amiddle distillate fuel oil, i.e. a fuel oil obtained in refining crudeoil as the fraction between the lighter kerosene and jet fuels fractionand the heavier fuel oil fraction. Such distillate fuel oils generallyboil within the range of about 100° C. to about 500° C., e.g. 150° toabout 400° C. The fuel oil can comprise atmospheric distillate or vacuumdistillate, or cracked gas oil or a blend in any proportion of straightrun and thermally and/or catalytically cracked distillates. The mostcommon petroleum distillate fuels are kerosene, jet fuels, diesel fuels,heating oils and heavy fuel oils. The heating oil may be a straightatmospheric distillate, or it may contain minor amounts, e.g. up to 35wt %, of vacuum gas oil or cracked gas oils or of both.

Heating oils may be made of a blend of virgin distillate, e.g. gas oil,naphtha, etc and cracked distillates, e.g. catalytic cycle shock. Arepresentative specification for a diesel fuel includes a minimum flashpoint of 38° C. and a 90% distillation point between 282 and 380° C.(see ASTM Designations D-396 and D-975).

The fuel oil may be an animal, vegetable or mineral oil. The fuel oilmay also contain other additives such as stabilisers, dispersants,antioxidants, corrosion inhibitors and/or demulsifiers.

The concentration of the additive in the oil may for example in therange of 1 to 5,000 ppm of additive (active ingredient) by weight perweight of fuel, for example 10 to 5,000 ppm such as 10 to 2000 ppm(active ingredient) by weight per weight of fuel, preferably 25 to 500ppm, more preferably 100 to 200 ppm.

The additive or additives should be soluble in the oil to the extent ofat least 1000 ppm by weight per weight of oil at ambient temperature.However, at least some of the additive may come out of solution near thecloud point of the oil in order to modify the wax crystals that form.

CONCENTRATES

The concentrates of the present invention are convenient as a means forincorporating the additive into bulk oil such as distillate fuel, whichincorporation may be done by methods known in the art. The concentratesmay also contain other additives as required and preferably contain from3 to 75 wt %, more preferably 3 to 60 wt %, most preferably 10 to 50 wt% of the additives preferably in solution in oil. Examples of carrierliquid are organic solvents including hydrocarbon solvents, for examplepetroleum fractions such as naphtha, kerosene, diesel and heater oil;aromatic hydrocarbons such as aromatic fractions, e.g. those sold underthe `SOLVESSO` tradename; paraffinic hydrocarbons such as hexane andpentane and isoparaffins; and bio-derived carrier liquids. The carrierliquid must, of course, be selected having regard to its compatibilitywith the additive and with the fuel.

The additives of the invention may be incorporated into bulk oil byother methods such as those known in the art. If co-additives arerequired, they may be incorporated into the bulk oil at the same time asthe additives of the invention or at a different time.

CO-ADDITIVES

The additive of the invention may be used in combination with one ormore additional cold flow improver additives, such as are known in theart (see, for example WO 93/14178), including comb polymers, polarnitrogen compounds, hydrocarbon polymers, and polyoxyalkylene compounds.

The additives of the invention may be used singly or as mixtures. Theymay also be used in combination with one or more co-additives such asknown in the art, for example the following: detergents, antioxidants,corrosion inhibitors, dehazers, demulsifiers, metal deactivators,antifoaming agents, cetane improvers, cosolvents, packagecompatibilisers and antistatic additives.

EXAMPLES

The following Examples, in which number average molecular weight (M_(n))are measured by gel permeation chromatography with polystyrene asstandard, illustrate the invention.

MATERIALS USED

Additive Components

A: an ethylene-vinyl acetate- versatic vinyl ester terpolymer, soldcommercially by Hoechst under the trade-name "Dodiflow-v-4159" in theform of a concentrate of 50% by weight active ingredient. The totalvinyl ester content measured by NMR was 37.9% by weight; the M_(n) byGPC was 3,600; and the number of methyl groups per 100 CH₂ groups was4.2.

"Versatic" is a trademark for a mixture of a cyclic and (mostly)tertiary acids containing 9-11 C atoms made by the action of carbonmonoxide and water on refinery olefins with an acid catalyst.

B: an ethylene-vinyl acetate copolymer of number average molecularweight 5000 as measured by GPC (Gel Permeation Chromatography) andcontaining 13.5% by weight of vinyl acetate in the form of a concentrateof 45% by weight active ingredient.

Formulations

The following formulations of A and B were prepared

    ______________________________________                   Weight Ratios    Formulation      A      B    ______________________________________    1                100    0    2                98     2    3                95     5    4                90     10    ______________________________________

Fuel Oil

A middle distillate petroleum fuel oil having the followingcharacteristics:

    ______________________________________           Density  0.8812           Cloud Point                    -5° C.           CFPP     -6° C.           IBP      180           Distillation           Characteristics           (D-86)           (all ° C.)           10%      226           20%      243           50%      280           90%      341           FBP      372    ______________________________________     IBP is initial boiling point     FBP is final boiling point

TEST METHOD (CFPP)

The CFPP test which is carried out by the procedure described in detailin "Journal of the Institute of Petroleum", Volume 52, Number 510, June1966, pp. 173-285, is designed to correlate with the cold flow of amiddle distillate in automotive diesels.

In brief, a sample of the oil to be tested (40 ml) is cooled in a bathwhich is maintained at about -34° C. to give non-linear cooling at about1° C./min. Periodically (at each one degree centigrade starting fromabove the cloud point), the cooled oil tested for its ability to flowthrough a fine screen in a prescribed time period using a test devicewhich is a pipette to whose lower end is attached an inverted funnelwhich is positioned below the surface of the oil to be tested. Stretchedacross the mouth of the funnel is a 350 mesh screen having an areadefined by a 12 millimeter diameter. The periodic tests are eachinitiated by applying a vacuum to the upper end of the pipette wherebyoil is drawn through the screen up into the pipette to a mark indicating20 ml of oil. After each successful passage, the oil is returnedimmediately to the CFPP tube. The test is repeated with each one degreedrop in temperature until the oil fails to fill the pipette within 60seconds, the temperature at which failure occurs being reported as theCFPP temperature.

TEST PROCEDURE

The above formulations (1 to 4) were each dissolved in samples of thefuel oil at a total concentration of 200 ppm by weight of additive perweight of fuel oil. The CFPP of each treated fuel oil sample wasmeasured immediately after treatment and then at successive weeklyintervals up to 4 weeks after the initial treatment.

    ______________________________________    RESULTS              TIME IN WEEKS    FORMULATION 0        1      2      3    4    ______________________________________    1           -18      -10    -12    -10  -13    2           -20      -18    -19    -18  -17    3           -21      -20    -19    -21  -19    4           -22      -20    -21    -20  -18    ______________________________________

The result show the deterioration (or regression) with time in CFPPperformance when additive A (formulation 1) was used alone, but thatinclusion of additive B (formulations 2-4) greatly reduced regression.Formulations 2 to 4 also showed excellent CFPP performance in comparisonto formulation 1, at equivalent points in time over the test period.

We claim:
 1. An oil-soluble additive comprising components (A) and (B)wherein(A) is an ethylene terpolymer having, in addition to unitsderived from ethylene, units of the formula: ##STR6## and units of theformula ##STR7## wherein R¹ and R², which may be the same or different,each represents H or methyl;R³ represents an alkyl group having up to 4carbon atoms; and R⁴ represents a tertiary alkyl group having 8 or morecarbon atoms; and (B) is an ethylene-unsaturated ester copolymer,different from (A), having a number average molecular weight (Mn) in therange of 1,200 to 20,000 and an ester content of 0.3 to 17 molar percent, provided that said ester content is at least 2 molar per centlower than that of the esters in (A), or any polyoxyalkylene cold flowadditive.
 2. The additive of claim 1 wherein R¹ represents hydrogen andR³ represents methyl.
 3. The additive of claim 2 wherein the units ofthe formula (II) are ##STR8## wherein OOCR⁴ represents neonanoate orneodecanoate.
 4. The additive of claim 1, wherein the total molarproportion of units of the formulae I and II in (A) is within the rangeof from 2.3 to 35 per cent.
 5. The additive of claim 1, wherein thenumber average molecular weight (Mn) of (A) is within the range of from3,000 to 6,000.
 6. The additive of claim 1 wherein the unsaturated esterforming the ethylene-unsaturated ester copolymer (B) is a vinyl ester.7. The additive of claim 1 wherein the proportion of (B) by weight,based on the weight of (A) and (B) combined, is 10% or less.
 8. Acomposition comprising a fuel oil and the additive as defined inclaim
 1. 9. An additive concentrate composition comprising the additiveas defined in claim 1 and a liquid carrier in admixture therewith.
 10. Acomposition comprising a fuel oil and the additive as defined in claim3.
 11. An additive concentrate composition comprising the additive asdefined in claim 3 and a liquid carrier in admixture therewith.
 12. Aprocess for inhibiting regression over time of the flowability of a fueloil composition as measured by the Cold Filter Plugging Point comprisingadding to the fuel oil an oil-soluble additive as defined in claim 1.13. A process for inhibiting regression over time of the flowability ofa fuel oil composition as measured by the Cold Filter Plugging Pointcomprising adding to the fuel oil an oil-soluble additive as defined inclaim
 3. 14. The process of claim 12 wherein the fuel oil is a middledistillate petroleum fuel oil.
 15. The process of claim 13 wherein thefuel oil is a middle distillate petroleum fuel oil.